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The methods used for highpressure/high-temperature (HP/HT) tool development are evolving, and development cycles are lengthening, particularly for ultra-HP/HT applications (those involving pressures greater than 15,000 psi or temperatures greater than 350°F) in which materials screening and stability assessments are required. What can the industry anticipate for future HP/HT wells in terms of architecture, product development, and regulatory challenges? This paper identifies current development paradigms and discusses the future challenges in well planning, product development, and regulation.

The technological challenges associated with the completion of wells at and above HP/HT conditions are diverse and continue to increase. Previous investigations into HP/HT projects identified technology gaps related to packers, bridge plugs, liner hangers, subsurface safety valves (SSSVs), tubing-to-packer seals, and related products. (Please see the complete paper for a comprehensive list of challenges faced in HP/HT environments, as well as a discussion of the historical perspective in HP/HT well development.)

In addition to the general challenge of materials design and testing for HP/HT environments, several specific component-based challenges also exist.

Packers. Packers and bridge plugs have been developed for service conditions as challenging as 500°F and 25,000 psi, but the primary difficulty in the development process today is the availability of materials, both metallic and nonmetallic, which are suitable for very high levels of stress and strain and which possess the desired corrosion resistance to achieve longevity requirements.

SSSVs. SSSVs contain many dynamic seals which must maintain their integrity and operating characteristics over the life of the completion. Also, the operator must have the capability to extend the life of a malfunctioning safety valve through the use of “insert valves.” These are smaller-diameter wireline-conveyed valves that can be run and inserted into the bore of the tubing-mounted safety valve so that production can continue under fail-safe conditions.

Liner Hangers. Liner hangers with integral packoff capabilities (packer-type expandable seals) have been developed for HP/HT applications. Typically, these tools are required to perform their sealing role to a gas-tight requirement. However, an industry specification tailored for the operational role of liner hangers does not yet exist.

Electronics. Conventional industrial and military electronic components are typically rated only to 125°C, far below the rating required for HT downhole electronics applications such as measurement-while-drilling and rotary-steerable systems in which they are used. Despite this, the oldest and largest consumer of electronics for HT applications is the downhole oil and gas industry.

Intelligent Monitoring and Production Systems. For downhole monitoring, electronic systems and fiber-optic (FO) systems are available. Electronic monitoring systems are marketed for use at 150°C and 30,000 psi, at which life expectancy is 10 years. Higher- temperature versions are currently marketed for use at downhole conditions as high as 175°C and 30,000 psi. At these conditions, life expectancy is only 5 years. FO monitoring systems are currently marketed for temperatures as high as 536°F at 20,000 psi. An important feature of FO systems is that they contain no electronic components; hence, they can operate reliably at much higher temperatures than electronic systems, and for much longer periods of time.

Intelligent production systems, sometimes referred to as intelligent-well systems, consist of flow-control valves, gauges, chemical-injection valves, and other components, and are used to control zonal production and act as platforms for monitoring systems. In general, these systems have been upgraded to “near-HP/HT” status. Commercially available electric systems on the market are rated for pressures up to 15,000 psi, but for sub-HP/HT temperatures, with life expectancy as high as 20 years.

HP/HT Challenges Specific to Well Intervention

Historically, discussions regarding technology gaps and challenges tend to focus on completion tools and systems. However, there are also significant challenges in well intervention.

Redundancy in Shoe-Track Isolation. Several Gulf of Mexico (GOM) operators have recently used advanced permanent bridge plugs for standalone barrier applications in ultra-HP/HT conditions to achieve redundancy in shoe-track integrity. These advanced permanent bridge plugs (sometimes referred to as isolation plugs) combine bridge-plug and production-packer technology to satisfy the need for ultra-HP/HT shoe-track isolation and life-of-the-well longevity.

Tubing Cutters. A variety of tubing cutters are available commercially. Some are effective into the ultra-HP/HT region, but few are known to be consistently effective in these applications. Jet cutters use a shaped-charge explosive to make the cut. A variety of charges can be used, and these models will be subject to (approximately) the same temperature limitations as perforating guns.

Chemical cutters operate by spraying a chemical through small ports in a tool body. In HP environments, their effectiveness is reduced by the backpressure effect (high hydrostatic pressure) on the chemical cutting fluid. At HP/HT conditions, chemical-cutter efficiency is well below 50%.

Radial torch cutters use energized plasma to make a cut. They are currently rated up to 500°F and 20,000 psi.

Mechanical cutters are limited by temperature because of the electronics and pressure owing to the housings that carry the electronics. Current technology can operate at 392°F and 20,000 psi. Mechanical cutters provide a controlled cut and generate only fine debris. The cut is controlled at surface, with the ability to modify the cut in real time.

Logging Tools and Electronics. Service life for printer-circuit-board (PCB) -based electronics packages at HP/HT conditions is very limited; at temperatures greater than 150°C, PCB life is measured in hours. A few new logging tools use hybrid or multichip modules and are rated at 175°C; their longevity is measured in days. At temperatures greater than 175°C, electronics usage is currently limited to a few passive logging tools, and longevity is measured in hours. These tools are passively cooled, which explains their short life span.

Miscellaneous Challenges. Several further significant intervention challenges exist in conveyance and fishing in HP/HT conditions, including work-string limitations, packer removal, temperature limitations of positive-displacement motors, and pressure and temperature limitations of ballistic setting tools.

Well Planning 

Systems-Integration Testing. Systems- integration testing for many applications can prove challenging, but is critical to the success of the completion or intervention. For example, an HP/HT bridge plug, HP/HT nonballistic hydrostatic setting tool, and an HP/HT casingcollar locator can each be validated separately, but integrating them and testing them as a system at downhole conditions is the so-called “acid test.”

Conveyance Methods. There are several methods to convey tools into a well. These methods include pipe, coiled tubing, and wireline (slickline and electric line). The decision to use one method over another will depend on many factors and will determine how the rig must be configured for the operation. At greater depths, it is preferred, when possible, to use wireline because this can reduce rig time significantly.

Hazard and Operability (HAZOP) Analysis. A HAZOP analysis is used to identify hazards and operational problems that may occur during well operations. Identifying potential hazards and operational problems correctly and having a plan in place and knowing the advantages and disadvantages of various options can ultimately help prevent loss of well control and can save lives. In an HP/HT application, a HAZOP analysis may prove useful in identifying contingency tools that need to be developed or tested before use in a well.

The Regulatory Landscape

Regulatory requirements vary globally and are beyond the scope of this paper. Instead, this section describes some of the Bureau of Safety and Environmental Enforcement (BSEE) requirements for US GOM waters.

Deepwater-Operations Plan (DWOP). All HP/HT completions require a new technology (NT) DWOP, regardless of water depth. BSEE regulators require that any NT that is technically complex, and that requires a high degree of specialized knowledge, be reviewed by an independent third party. If the NT exceeds the limit of existing standards, industry experts and the BSEE must discuss the matter and achieve a high degree of convergence. If the NT conflicts with existing engineering standards, the BSEE will not approve its use.

NTDWOP Process for HP/HT Applications. The BSEE recommends that the well operator contact the Technical Assessment Section of the BSEE as early as possible concerning an HP/HT project to receive up-to-date guidance. For any NT, an NT Conceptual DWOP must be submitted with a complete list of all equipment and materials that will be used in the HP/HT well along with the proposed engineering standards that will be used to evaluate materials selection and design-verification analysis, and perform validation testing. After the development of the NT is complete, the NT DWOP submittal must contain all the analysis and test reports proposed in the NT Conceptual DWOP (see the complete paper for a description of these elements).

Design Verification and Analysis. The BSEE currently defaults to API PER 15K and API 17 TR8for guidance on HP/HT material selection, design-verification analysis, and validation testing. However, the BSEE does not consider these documents to be all-inclusive or complete.